We present a study of the L2 acquisition of Spanish Differential Object Marking (DOM) by L1 English speakers. We tested adult native English speakers living in Spain (n=30), in contrast to an adult control group of native Spanish speakers (n=71). Subjects completed a grammaticality judgment task, an elicited production task, and a discourse context-matching task, each of them manipulating several syntax-semantics features influencing the realization of DOM. Our results are argued to be consistent with the Feature Reassembly Hypothesis (Lardiere 2009), according to which the difficulty of L2 acquisition is linked to the amount of reassembly of features required. In particular, we argue that L2 subjects have difficulty acquiring the feature bundle [+animate, +specific], but perform better when only one of the two features is sufficient to determine the presence or absence of DOM.